The primary goal of this project is to design and implement a multi- institutional, open-label phase I/II study of hydroxurea (HU) therapy in children with Sickle Cell Disease. To achieve the main goal, the project has four specific aims: a) To determine if HU will elevate the concentration of fetal hemoglobin, hematocrit and red cell mean corpsucular volume in children with Sickle Cell Anemia between the ages of 5 and 18 years old. b) To determine if the therapeutic dose of HU in pediatric patients is similar to that in adults. c) To determine if the hematologic and renal toxicities in chidlren are similar to those in adults. d) To determine if there are adverse effects on growth in children taking HU. To date, a total of 13 patients have now completed the study. Two patients were discontinued from the study over the past year; one moved from the area and the other was discontinued for non-compliance. Phase I/II will be completed March 31, 1998. Phase III, in which we will follow-up patients for five years, is planned to begin in April, 1998.